/Engine/Source/Runtime/GeometryCore/Public/Curve/CurveUtil.h
the tangent direction (normalized) of the path at Idx, using the surrounding vertices (as found byGetPrevNext())
namespace UE { namespace Geometry { namespace CurveUtil { template<typename RealType, typename VectorType> VectorType UE::Geometry::CurveUtil::Tangent ( const [TArrayView](API\Runtime\Core\Containers\TArrayView)< const VectorType > & Vertices, int32 Idx, bool bLoop ) } } }